The present invention relates to an apparatus and method for controlling the temperature of LPG (Liquid Petroleum Gas) fuel and in particular for not only cooling the fuel but also keeping it at a relatively constant cool temperature before it enters the combustion chamber of an engine.
Liquid gas, such as LPG, is a common fuel used in many internal combustion engines. The LPG is for reasons of practicability stored in its liquid state. To use LPG as a fuel for internal combustion engines hence requires conversion from the liquid to the gas state. This is accomplished in a liquid to gas converter that is well known in the art.
However, the conversion step from a liquid phase to a gas phase creates a refrigerative effect, which, if left unheated, will cause the converter to freeze. This in turn causes the regulator jet in the converter to block preventing supply of fuel to the engine. The degree of cooling obviously increases with greater flows of gas such as when the engine is under load or accelerating.
Current solutions to this problem include heating the converter. Typically the heat is provided from the cooling means of the engine, such as the engine radiator, where hot coolant is piped from the engine to then pass through the converter. This has been successfully used for a number of years and creates a hot gaseous fuel for the engine. The temperature of the heated gaseous fuel can be in the range of 40° C. to 90° C. or higher, depending on coolant temperature and the rate of gas conversion.
One of the difficulties of heating the converter in this way is that the fuel is relatively “hot”. It has been found that high temperature fuels can cause a loss of power and an increase in fuel consumption due to inefficient burning of the fuel. The air/fuel mix is less dense at higher temperatures and less mixture enters the cylinders producing less power and less efficient burning of the mixture.
A further difficulty with a hot mixture is unstable firing of the fuel in the engine cylinders.
In addition, large fluctuations in fuel density cause a corresponding change in the air/fuel ratio causing either a lean or rich mix depending on the combination of conditions.
Devices that cool the air before it is injected into the combustion chamber are known. These however are generally large and limited in application and do not represent a commercially viable option.
Yet other devices attempt to cool the fuel/air mixture before injection. These are usually an integral part of the converter. Typically they utilise a mechanical thermostat for coolant flow control wherein the thermostat reduces the flow of coolant when at a certain temperature. They however only measure the coolant temperature. The gas temperature is not measured and it is only assumed that it is at a more effective operating temperature. However, varying gas flows will vary the gas temperature greatly due to excessive thermal lag in changes in gas temperature reaching the thermostat that is embedded in the coolant in the heating chamber. These devices can also not be retrofitted to existing engines and converters.
Accordingly none of the prior art devices teach one that by controlling the gas temperature better fuel performance can be gained. In fact, most of them teach operating temperatures that are relatively high, and well above those at which performance improves.
It is an object of the present invention to propose an apparatus that overcomes at least some of the abovementioned problems or provides the public with a useful alternative.
It is a further object of the present invention to provide an apparatus that enables the operation of the converter at a significantly lower temperature. This provides a low temperature fuel to the engine's carburettor, thus cooling the fuel/air mixture. Running an engine on a cooler fuel/air mixture provides an increase in power and a greater efficiency in fuel use, therefore greater economy. It also aids in reducing knock and detonation in the engine and creates an improved burn of the mix. Further, by maintaining the temperature in a narrower band there is less variation in the fuel mix.
This is achieved by utilising the refrigerative effect of the conversion of liquid gas fuel, combined with controlling the gas temperature and heating of the converter, to take advantage of the properties of a low temperature fuel/air mix.
In its most basic form the invention utilises a module for the provision of low temperature gaseous fuel to a liquid cooled internal combustion engine by closed loop control of the converter temperature. A module also controls the amount of hot coolant from the engine cooling system flowing through the liquid gas converter in order to operate the converter at lower than coolant temperatures.